fix: correct Python version mismatch in Dockerfile

[shitalm]

Problem

The Dockerfile had a Python version mismatch between the builder stage (Python 3.12) and the runtime stage (Python 3.13), causing ModuleNotFoundError when running Docker containers.

Solution

Changed the runtime image from python:3.13-slim-bookworm to python:3.12-slim-bookworm to match the builder stage version.

Changes

• Updated Dockerfile line 25 to use python:3.12-slim-bookworm
• Ensures venv compatibility between builder and runtime stages

Testing

• Docker containers now start successfully without ModuleNotFoundError
• Virtual environment works correctly with matching Python versions

Related

Fixes the issue where Docker containers fail with ModuleNotFoundError: No module named 'postgres_mcp'

[neverinfamous]

🎉 Thank you so much @shitalm for this contribution!

You're absolutely right - we had a Python version mismatch between the builder stage (3.12) and runtime stage (3.13). This is our first external contribution across all five of our public projects, and we really appreciate you taking the time to identify and fix this issue!

Review Summary:
✅ Correct diagnosis - The mismatch was causing ModuleNotFoundError due to venv incompatibility
✅ Proper fix - Changing runtime to python:3.12-slim-bookworm matches the builder stage
✅ Well documented - Clear problem/solution description with testing notes

The irony is that lines 26-28 of the Dockerfile even have a comment warning about this exact scenario! 😅

We'll merge this right away and it will be included in our next release.

Welcome to the postgres-mcp community! 🚀